The resolution is not in plural terms but refers to a single case of moral permissibility.
The resolution asks us if it is ever morally permissible to kill one innocent person in order to save more innocent people – not if it is always morally permissible to do so.
If the resolution wanted us to discuss a universal moral principle it would say “It is always morally permissible to kill one innocent person” or “Situations where killing one innocent person to save more innocent people are morally permissible”.
Thus, the affirmative burden is to prove that it can be morally permissible to kill one innocent person to save the lives of more innocent people. If I can show you one example where this is possible, I win today’s round.